The present invention relates to an apparatus and method for controlling the rate of composition change of a fluid having a changing composition. More particularly, it relates to an apparatus and method for controlling the rate of composition change of fuel in a vehicle capable of using fuels of differing composition.
It is well known that ever tighter emissions regulations and petroleum depletion have prompted research into the feasibility of using alternative fuels in motorized vehicle engines. Currently, ethanol/gasoline and methanol/gasoline mixtures are among the alternative fuel possibilities being considered.
Alternative fuel mixtures exhibit physical properties and performance characteristics which are different from pure gasoline, including dissimilar combustion burn rates, volumetric energy content, vapor pressures, octane ratings, and heats of vaporization. The operating parameters of vehicle engines utilizing alternative fuels must be adjusted to accommodate such differences in order for the engines to operate efficiently. The operating parameters which must be adjusted include the air bypass, fuel flow, spark timing, and air/fuel ratio.
The aforementioned adjustments can be made automatically by an engine control computer. Engine control computers are well known and are commonly used in vehicles. See, for example, U.S. Pat. No. 4,706,630 to Wineland et al. However, in order for an engine control computer to correctly make the requisite adjustments, the instantaneous composition of the fuel being burned in the engine must be known by the computer. To the extent that fuel composition information sent to the engine control computer differs from the actual composition of fuel being burned in the engine, adjustments made to the engine will be improper. Improper engine adjustments, in turn, can result in poor engine performance and excess emissions due to incomplete combustion. Thus, a close correlation between the composition of fuel actually being burned in an engine and that which is made known to the engine control computer is needed to facilitate the use of alternative fuel use in motorized vehicle engines.
A common method of providing fuel composition information to engine control computers is through the use of in-line fuel sensors which exploit differences in physical properties between gasoline and ethanol or methanol to measure the instantaneous composition of fuel flowing past the sensor. The sensor then sends a signal to the computer which corresponds to the composition of the fuel flowing past the sensor.
A frequently encountered problem with alternative fuel vehicles is rapid composition change of the fuel flowing from the fuel tank to the engine. The fuel in alternative fuel vehicles will typically consist of multiple components, such as combinations of gasoline, methanol and ethanol. In addition, the fuel may also contain various fuel additives or water. Prior to the complete mixing of the fuel by the fuel pump as it circulates fuel through the fuel system, "pockets" of fuel having varying compositions will flow in the fuel line towards the engine, thus introducing rapidly and continuously varying compositions of fuel to the engine. As will be explained, engine control systems cannot adequately cope with such rapid composition changes. The rate of fuel composition change is particularly severe when phase separation occurs or when the fuel tank is nearly empty and a different blend is added.
Phase separation in the fuel tank and in the fuel system occurs when the weather is cold and/or the water content of the fuel blend is above its threshold of tolerance for the current temperature. In this instance, when the vehicle's engine is not running such that the fuel is not flowing but is stationary in the fuel tank and fuel system, the fuel will separate into two or more immiscible phases. The higher density methanol rich, ethanol rich, or water rich phase will settle towards the lower portions of the fuel tank and fuel system while the lower density gasoline rich phase will accumulate towards the upper portions of the fuel tank and fuel system. When the engine is subsequently started and the fuel pump resumes circulating fuel through the fuel system, the phase separated mixture will form an emulsion as it begins to mix. Prior to forming an emulsion, the composition of the fuel being sent to the engine changes very rapidly. After the emulsion forms, the rate of composition change slows but is still higher than the rate at which engine control systems can adequately control the performance of the engine due to inadequate mixing of the emulsion.
Another situation in which a high rate of compositional change is encountered is when a vehicle has been operating on one fuel blend, the fuel tank is nearly empty, and a fuel blend having a very different composition than the previous blend is added, the composition of the fuel in the fuel tank will mix to form a fuel having a composition close to that of the added blend. When the engine is started, the fuel system (i.e. fuel lines, fuel pump, fuel filter, etc.) will initially be full of the previous blend. After a short time, the new blend will enter the fuel system from the fuel tank, causing the rate of composition change of the fuel reaching the engine to temporarily be much higher than is controllable by the engine control system.
When the rate of fuel composition change is high, particularly after phase separation or fuel blend change on an empty tank, engine control systems utilizing an engine control computer/fuel sensor arrangement are unable to keep up with the changing composition. This is due, in part, to the distance separating the fuel sensor and the engine. When the fuel composition is changing rapidly, the fuel composition information being sent to the engine control computer, based on the instantaneous composition of fuel flowing past the sensor, will differ from the composition of fuel actually being introduced into the engine. The result will be improper engine adjustments being made by the engine control computer, resulting in poor engine performance and excess emissions.
Accordingly, it is seen that a need exists in the art for a means of controlling the rate of composition change of a fluid having a changing composition, particularly when that fluid is a fuel in an alternative fuel vehicle.